1. Field of the Invention
The present invention relates to an apparatus capable of detecting a small-size object or a small target area of an object, and more particularly to an apparatus with a combination of a point light source and a single lens.
2. Description of the Prior Art
The quantification of chemical and biochemical components in colored aqueous fluids, in particular colored biological fluids such as whole blood and urine and biological fluid derivatives such as serum and blood plasma, is of ever-increasing importance. Important applications exist in medical diagnosis and treatment and in the quantification of exposure to therapeutic drugs, intoxicants, hazardous chemicals and the like. In some instances, the amounts of materials being determined are either so miniscule in the range of a microgram or less per deciliter or so difficult to precisely determine that the apparatus employed is complicated and useful only to skilled laboratory personnel. In this case the results are generally not available for some hours or days after sampling. In other instances, there is often an emphasis on the ability of lay operators to perform the test routinely, quickly and reproducibly outside a laboratory setting with rapid or immediate information display.
One common medical test is the measurement of blood glucose levels by diabetics. The diabetic patients usually measure their blood glucose level from two to seven times a day depending on the nature and severity of their individual cases. Based on the observed pattern in the measured glucose levels, the patient and physician together make adjustments in diet, exercise and insulin intake to better manage the disease. Clearly, this information should be available to the patient immediately.
In a method currently and widely used, a sample of fresh whole blood (typically 20˜40 μl ) is placed on an ethylcellulose-coated reagent pad containing an enzyme system having glucose oxidase and peroxidase activity. The enzyme system reacts with glucose and releases hydrogen peroxide. The pad also contains an indicator that reacts with the hydrogen peroxide in the presence of peroxidase to give a color proportional in intensity to the sample's glucose level. Another popular blood glucose test method employs similar chemistry but in place of the ethylcellulose-coated pad employs a water-resistant film through which the enzymes and indicator are dispersed.
In both cases the sample is allowed to remain in contact with the reagent pad for a specified time (typically one minute). Then in the first case the blood sample is washed off with a stream of water while in the second case it is wiped off the film. The reagent pad or film is then blotted dry and evaluated. The evaluation is made either by comparing color generated with a color chart or by placing the pad or film in a diffuse reflectance instrument to read a color intensity value.
While the above methods have been used in glucose monitoring for years, they do have certain limitations. The sample size required is rather large for a finger stick test and is difficult to achieve for some people whose capillary blood does not express readily.
In addition, these methods share a limitation with other simple lay-operator calorimetric determinations in that their result is based on an absolute color reading, which is in turn related to the absolute extent of reaction between the sample and the test reagent. The fact that the sample must be washed or wiped off the reagent pad after the timed reaction interval requires that the user be ready at the end of the timed interval and wipe or apply a wash stream at the required time. The fact that the reaction is stopped by removing the sample leads to some uncertainty in the result, especially in the hands of the home user. Overwashing can give low results and underwashing can give high results.
Another problem that often exists in simple lay-operator calorimetric determination is the necessity for initiating a timing sequence when blood is applied to a reagent pad. A user will typically have conducted a finger stick to obtain a blood sample and will then be required to simultaneously apply the blood from the finger to a reagent pad while initiating a timing circuit with his or her other hand, thereby requiring the use of both hands simultaneously. This is particularly difficult since it is often necessary to insure that the timing circuit is started only when blood is applied to the reagent pad. Both of the prior methods require additional manipulations or additional circuitry to achieve this result.
Accordingly, it is an intention to provide means for monitor a content of a specific component in a colored fluid such as a blood sample, which can overcome the drawbacks of the prior methods.